A semiconductor light emitting device using a high-intensity light emitting element such as an LED (Light Emitting Device) has attracted attention as a light source of an illumination apparatus. The semiconductor light emitting device includes at least one light emitting element mounted in a plane of a light emitting element mounting member and emits light by a current supplied externally. The illumination apparatus is, for example, a backlight for a liquid crystal display apparatus.
In order to utilize the semiconductor light emitting device as the light source of the illumination apparatus, it is necessary to efficiently extract the light emitted from the semiconductor light emitting device to a side thereof facing an object to be irradiated (For example, an LCD panel in case of a backlight for a liquid crystal display apparatus).
However, the light emitting element emits light from an upper surface and a lateral surface of the light emitting element. In other words, the light emitting element emits light, from the upper surface of the element, not only in a substantially parallel direction but also in an oblique direction with respect to an optical axis (an axis passing through a center point of the light emitting element and, moreover, the axis being perpendicular to the surface of the semiconductor light emitting device where the light emitting element is mounted).
In this way, the light emitted from the light emitting element does not always travel along the optical axis. Accordingly, much of the light cannot be utilized, and light utilization efficiency of the semiconductor light emitting device decreases.
In order to solve the problem, (i) light emitted from the lateral surface of the light emitting element in the perpendicular direction with respect to the optical axis and (ii) light emitted from the upper surface of the light emitting element in an oblique direction with respect to the optical axis must be refracted in a direction of the optical axis. An arrangement for refracting the light emitted from the light emitting element in the direction of the optical axis is disclosed in: Japanese Unexamined Patent Publication (Tokukai 2005-5437 (published on Jan. 6, 2005)), Japanese Unexamined Patent Publication (Tokukai 2004-128241 (published on Apr. 22, 2004)), Japanese Unexamined Patent Publication (Tokukai 2002-141558 (published on May 17, 2002)), Japanese Unexamined Patent Publication (Tokukai 2005-150408 (published on Jun. 9, 2005)), and USP No. 2004/0257797 A1 (Date of patent: Dec. 23, 2004).
The five documents above disclose an semiconductor light emitting device having at least one depressed section(s) on a light emitting element mounting member, wherein an inner wall surface of the depressed section forms a reflection surface having a predetermined angle with respect to the optical axis and every depressed section mentioned above has the light emitting element provided in it.
As illustrated in FIG. 10, conventionally, among semiconductor light emitting devices in which the light emitting element is assembled in a package with a lead terminal and the like, there is a high-power semiconductor light emitting device 101 including a large sized element whose power consumption is particularly high. In the high-power semiconductor light emitting device 101, the light emitting element is assembled via a submount on a heat dissipation member for heat dissipation.
In order to reflect the light, which is emitted from the upper surface of the light emitting element in the oblique direction, as much as possible by means of the reflection surface, it is necessary to make the depressed section deep to a certain extent. However, the reflection surface has the predetermined angle with respect to the optical axis. Accordingly, the deeper the depressed section becomes, the larger a diameter of an opening of the depressed section on the upper surface of the light emitting element mounting member becomes.
Therefore, in the conventional arrangement, the light emitting elements cannot be mounted close to each other on one light emitting element mounting member. When only a small number of the light emitting elements can be mounted on one light emitting element mounting member in this way, many semiconductor light emitting devices are needed to constitute a light source device having light intensity equivalent to a light source device including many light emitting elements. As a result, the light source device becomes very large.
In addition, in the conventional arrangement, in a case where the angle of the reflection surface with respect to the optical axis is arranged to be small so as to decrease the diameter of the opening of the depressed section on the upper surface of the light emitting element mounting member, it becomes difficult to reflect the light emitted from the lateral surface of the light emitting element in the direction of the optical axis, as illustrated in FIG. 9. Therefore, an original purpose of the reflection surface cannot be achieved.